A sampling filter that chronologically discretizes a signal, to thus perform frequency conversion and filtering, is used in a radio communication device for mobile communications or the like. A sampling filter, such as that described in connection with Patent Document 1, has hitherto been available as a related-art sampling filter. FIG. 7 shows a related-art sampling filter described in connection with Patent Document 1.
In FIG. 7, the related-art sampling filter has a switch 2A, a switch 2B, an integrator 3, a weighting and sampling (W&S) element 6, and a control signal generator 7. Processing pertaining to three processes; namely, a reset process, a sampling process, and a holding process, is performed by a clock signal, a reverse clock signal, a W&S signal, and a reset signal which are generated by the control signal generator 7.
A filtering characteristic of the sampling filter is determined by a weighting function. Further, the weighting function is dependent on a combination of the W&S element 6 and a W&S signal, and the W&S signal conforms to; for example, three weighting functions (a constant function, a gradient function, and a Gaussian function). A signal current passing through the W&S element 6 is zero outside a sampling window and weighted in the sampling window in accordance with a weighting function (the constant function, the gradient function, and the Gaussian function). Thus, the filtering characteristic can be altered by weighting an output from the W&S element 6 by means of the W&S signal.
Patent Document 1: JP-T-2003-510933 (pg. 31, FIG. 2A)